Because the symptoms of colon cancer are vague and typically occur
late in the development of the cancer, a variety of tests are used to
both screen and diagnose the disease. Screening tests look for disease
in those who look and feel healthy, ideally catching the disease as
early as possible or in the case of colon cancer, even before the
precancerous lesion has turned into cancer. Diagnostic tests look for
the cause and determine the extent of the disease in someone who has
obvious symptoms.

A bowel prep is often required in preparation for many of these
tests, especially a colonoscopy. This involves cleaning out your bowel
the night before the test with a prep solution such as
"GoLYTELY." It is important that the bowel be clean so the
physician performing the colonoscopy or barium enema gets the best look
at your colon. Since some preps can affect your blood level for certain
electrolytes, your health care professional will tell you which prep to
use for your procedure.

Diagnostic Tests

Flexible sigmoidoscopy or colonoscopy. If a mass or any other types
of abnormal areas are seen through the flexible sigmoidoscope or
colonoscope, a sample (biopsy) is taken for further examination by a
pathologist to determine if it's cancerous or benign.

Complete blood count (CBC) and blood chemistry. The CBC determines
whether you are anemic because many people with colorectal cancer become
anemic due to prolonged bleeding from the tumor. This test is also
performed on a regular basis in people receiving chemotherapy because
these drugs temporarily affect blood-forming cells of the bone marrow.

Carcinoembryonic antigen blood test (CEA) . The CEA blood test is a
marker for colon cancer used to check for cancer in people who have
already been treated for colorectal cancer. Not all colon cancers
increase CEA blood levels, but it can provide an early warning of a
cancer that has returned.

Ultrasound. This test uses sound waves reflected off the tissues of
nearby organs and converted by computer into images to help your health
care professional see if any mass exists. Ultrasound may be used to look
at your liver or inside your bowel for tumors.

Computed tomography (CT) . In this test, a rotating X-ray beam
creates a series of pictures of the body from many angles, helping
visualize any masses.

Magnetic resonance imaging (MRI) : Like CT, magnetic resonance
imaging displays a cross-section of the body. However, MRI uses powerful
magnetic fields and radio waves instead of radiation. MRI is used to
examine the liver or to stage rectal cancer.

Chest x-ray. This familiar imaging test detects if colorectal
cancer has spread to the lungs.

PET scanning: This test can determine if certain cells are using
glucose more than other cells. Cancer cells, which are actively
dividing, use more glucose so they light up on a PET scan. This test is
used to follow cancer and can be combined with a CT scan to better
localize a possible recurrence. It is important to remember that not all
tumors will be responsive to PET/CT imaging.

Colorectal Cancer Stages

As with all cancers, there are various stages of colon cancer:

Stage 0: Abnormal (dysplastic) cells have been found in the
innermost lining (mucosa) of the colon. This stage is also known as
carcinoma in situ or intramucosal carcinoma, and there is a very small
chance these cells will spread, so this stage is not considered to be
invasive cancer.

Stage I: Cancer has spread to the inside lining of the colon but
not to the outer walls.

Stage II: Cancer has spread through the colon or rectum and may
invade surrounding tissue, but no lymph nodes are involved.

Stage III: Cancer has spread to the lymph nodes, but not to distant
sites.

Stage IV: Cancer has spread to other distant parts of the body,
such as the liver or the lung.

"What's New in Colorectal Cancer Research and
Treatment?" The American Cancer Society. March 7, 2006.
http://www.cancer.org. Accessed March 9, 2006.

"Colorectal cancer: early detection." The American Cancer
Society. February 2006. http://www.cancer.org. Accessed March 2006.

"New Recommendations by the American College of
Gastroenterology Call for Changes in Colorectal Cancer Screening of
African Americans." The American College of Gastroenterology. March
2005. http://www.acg.gi.org. Accessed March 2006.